Phosphors of alkaline earth yttrium and lanthanum phosphates silicates with an apatite structure had been prepared by Wanmaker et al. and described in the Journal of Solid State Chemistry 3, 452-457 (1971) in which they described a double firing process at temperatures between 1200.degree. and 1500.degree. C. The first firing was for two hours at 1350.degree. C., the reaction products being ground, sieved and refired for two hours at 1350.degree. C. The samples were prepared in air, but for cerium and tin activation a slightly reducing atmosphere was used. In a paper by Isaacs entitled A Study for Eu.sup.3+ Fluorescence in Some Silicate Oxyapatites, discusses the intense red luminescence seen when europium 3+ activated strontium yttrium silicate oxyapatite was excited with a 313 nm radiation.
Silicate apatites are hard, stable materials and lend themselves to a variety of compositional substitutions. The silicate oxyapatites prepared by Issacs were fired in air at approximately 1300.degree. C. for a period of four hours. In addition to the europium activated strontium silicate oxyapatites, Isaacs studied the calcium and manganese analogs.